Many aircraft are powered by jet engines. In most instances, jet engines include one or more gas-powered turbine engines, auxiliary power units (APUs), and/or environmental control systems (ECSs), which can generate both thrust to propel the aircraft and electrical energy to power systems installed in the aircraft. Although most aircraft engines are generally safe, reliable, and efficient, the engines do exhibit certain drawbacks. For example, the turbine engines, as well as other components that make up the engine, can be sources of unwanted noise, especially during aircraft take-off and landing operations. Moreover, APUs and ECSs can be sources of unwanted ramp noise. Thus, various governmental rules and regulations aimed at mitigating such noise sources have been enacted.
To address, and at least somewhat alleviate, the unwanted noise emanating from aircraft noise sources, and to thereby comply with the above-noted rules and regulations, various types of noise reduction treatments have been developed. For example, one type of noise reduction treatment that has been developed for use in aircraft ducts is a noise suppression panel. In many instances, noise suppression panels are flat or contoured, and include a honeycomb structure disposed between a backing plate and a face plate. Other noise suppression materials and structure may also be disposed between the backing plate and face plate. The noise suppression panels are typically placed on the interior surface of engine or APU inlet and/or outlet plenums, as necessary, to reduce noise emanations.
Although the above-described noise suppression panels do exhibit fairly good noise suppression characteristics, the panels also exhibit certain drawbacks. For example, the honeycomb structure can be costly to manufacture, and difficult to conform to contoured surfaces. The honeycomb structure can also be difficult to bond to the backing plated and/or face plate. Moreover, the honeycomb structure used in these panels is typically uniform in size and shape, which can result in the noise suppression panel being highly effective over only a relatively narrow frequency range.
Hence, there is a need for a noise suppression panel that is less costly to manufacture as compared to known panels, and/or can be readily conformed to contoured surfaces, and/or can be readily bonded to backing and/or face plates, and/or is effective over a relatively wide frequency range. The present invention addresses one or more of these needs.